Embodiments of the present invention relate to a projection display. Further embodiments of the present invention relate to a method for displaying an overall image. Further embodiments relate to a computer program for performing the method for displaying an overall image. Further embodiments of the present invention relate to an array for manipulating the mapping characteristics of a projection apparatus for different projection distances. Further embodiments of the present invention relate to a projection display having a non-circular and/or elongated overall aperture.
A projection display or projection system can be used to project an image or pattern onto a projection area, such as a screen or an object. Thereby, the image or pattern can be essential static, at least for a longer time span, as is known from a slide projector. Another type of a projection display is known as a video projector or digital projector and is able to project also dynamic images or image sequences. Projection displays or projection systems are also used in 3D measuring or surveying systems based on the principle of fringe projection or generally the projection of one or several known patterns onto an object to be measured.
In order to project the image or pattern in a focused manner onto the projection area, the projection area should be possibly at a distance from the projection display or system onto which the projection optics of the projection display is focused, or be at least within a tolerance range around this distance. This tolerance range is also referred to as a screen-sided depth of focus of the projector or projection display. In many projection displays, the focal length of the projection optics can be adjusted manually or automatically to the present or desired distance between projection display and projection area. However, it can be the case that the projection area is oblique to a projection direction predetermined by the projection optics, whereby the distance between the projection display and the projection area can change greatly within the image. For example, a bottom edge of the projected image can be at a much shorter distance to the projection display than a top edge of the same projected image. In a curved, discontinuous or stepped projection area, also, large distance variations can result within the projected image. Possibly, this distance variation can be greater than the screen-sided depth of focus which the projection display can obtain. In this case, even with optimum focusing of the projection optics, it has to be taken into account that individual areas of the projected image appear out of focus or blurred.
Greater depth of focus can typically be obtained by a higher f-number. However, a higher f-number also reduces the effective area available for light transmission. Thus, an increased f-number is typically accompanied by lower luminosity, which typically causes other problems, in particular when providing a sufficiently strong light source for the projection display.
With respect to a desired miniaturization of projection displays having sufficient luminosity, the usage of multi-channel optics has been suggested. DE 10 2009 024 894 describes a projection display having a light source and evenly spaced optical channels. By a slightly reduced pitch of the projection lenses with respect to the imaging structures, an offset of the respective imaging structure and the respective projection optics increasing from the array center towards the outside results, so that superposition of the real individual mappings at a finite distance results. Due to the separation into several channels, it is possible to reduce the distance between imaging structure and projection optics, i.e. the structural height, so that miniaturization is obtained together with other advantages. In the projection display described in DE 10 2009 024 894, the evenly arranged optical channel result, however, in a symmetrically designed overall aperture, which is why the depth of focus range is accordingly arranged symmetrically.
Depending on the field of application of the projection display, previous knowledge about the image(s) to be projected, or at least an image feature contained therein, already exists. In the case of fringe projection for 3D measuring of objects, for example, the orientation of the fringe patterns is known. This results in different requirements on the depth of focus to be obtained by the projection display for a first direction running, for example, essentially parallel to the fringes of the fringe pattern and a second direction running, for example, essentially orthogonally thereto.